In the automotive industry fiber felt materials are used in a broad range of products for sound insulation for instance in doors, roof lining, the floor area or as inner dash cladding. These products are formed and cut from large felt blanks to fit in the available space. Certain areas of such parts need higher amounts of material to obtain locally higher noise attenuation. In particular, the inner dash situated inside the passenger compartment and covering the wall between the engine bay area and the passenger compartment as well as certain areas of the floor covering have areas of increased fiber density. Felt products can be combined with other materials like mass layer to form a spring mass system or they can be used on their own to function as an acoustic absorbing layer. In all cases they can also be combined with aesthetic or acoustic covering layers, like thin nonwoven, needle punch or tufted carpets. These products need to follow the shape and contour of the area they need to cover as well as need to have fiber free areas for instance for fastening means and to go around appliances in a vehicle.
Fiber-felt products are classically produced from preformed constant density fiber mats containing binder fibers or resins, which are pressed in a heated mold and cut to obtain the desired form and stiffness. A disadvantage of this method is that the grammage of the product depends on the density of the fiber mat and is therefore restricted, either the density of the mat used is too high for most of the surface area molded or areas with a higher grammage can only be achieved by additionally supplying the material by hand. This is time consuming and/or very expensive. Furthermore because the fiber mats are delivered as a roll good or as pre-cut mats the production process is bound to render a lot of scrap material. Another disadvantage of the use of preformed fiber mats is that they easily tear or break when they are pressed in more extreme contoured molds. As the products can only be cut after a binding step, the scraps after cutting are of mixed heat set material that cannot be used anymore in the process. The material is due to its mixed nature difficult to recycle. This is a real problem for the automotive industry.
WO 2007/134812 describes an apparatus and a method for manufacturing non-woven products. The apparatus comprises a rotating drum on which a material shaping area in the form of a mold cavity is provided. The mold cavity corresponds to the negative form of the wanted product. Within the drum, vacuum means are provided in order to suck air through openings in the wall of the mold cavity. Fiber material is fed to the mold cavity by means of a fiber feed device. The fibers and hence the wanted product formed thereof are held in the mold by a negative pressure applied to the mold cavity, i.e. the material is held in the mold by the suction airflow while the drum is rotating and is carrying the mold cavity to a transfer device at which the formed material is de-molded. The vacuum compacts the fibers enough to keep a certain shape, however upon demolding the shape will flatten out as there is no real binding between the fibers. This effect can worsen when synthetic fibers are used alone or in a blend as they are smoother and slide easier.
After the de-molding step the formed unbonded material can be supplied to a further mold, particularly a compression mold or can be directly subjected to a heat treatment in a through hot air oven. In the further molding step a non-woven product with a final shape is formed from the formed material by applying heat and pressure.
The described method and apparatus has the advantage that at least the formed material can be manufactured in a continuous manner by means of continuous rotation of the drum. However, as the formed material often consists of unbonded fibrous material, the handling of the formed material during and after the de-molding step until it is heat set is delicate. During this process period the formed material can likely lose its wanted shape or even be disintegrated. In particularly fiber free areas will fill up again during demolding. Furthermore the instable structure of the formed material is difficult to put in a follow-up mold precisely as a correction after lay down is not possible anymore. Slight offsets can occur and the product finally produced is prone to rejection at quality control, for not fitting the three-dimensional shape asked for.